(a) Field of the Invention
The present invention relates to thin, resin-encapsulated semiconductor devices for surface mounting wherein large scale Si chips are encapsulated.
(b) Description of the Related Art
Semiconductor elements such as IC and LSI are being scaled up as the degree of integration increases, while resin-encapsulated semiconductor devices are being increasingly down sized and thinned. Further, in recent methods for mounting semiconductor devices on boards, the semiconductor devices themselves are heated rapidly to high temperatures of 200.degree. C. or higher. At that time, water contained in resin encapsulating materials evaporates, and the vapor pressure acts as separating stress between the resin encapsulating materials and insert members, such as the semiconductor devices or lead frames, to cause separation between the resin encapsulating materials and the insert elements, and particularly, in thin and flat package type resin-encapsulated semiconductor devices, to cause blisters or cracks. There have been some attempts to solve such problems. For example, conventional resin encapsulating materials containing as a filler for decreasing moisture absorption 50 to 60% by volume of crystalline silica, fused silica or a mixture thereof are replaced by resin encapsulating materials containing as the filler 65 to 90% by volume of fused silica alone. It is also attempted to improve adhesion to insert elements by replacing the o-cresol novolac epoxy resins contained in conventional resin encapsulating materials with the epoxy resins represented by the following general formula (I) or a mixture thereof with o-cresol novolac, or by replacing the phenolic novolac resins used as curing agents in conventional resin encapsulating materials with the aralkyl phenolic resins represented by the following general formula (II).
The occurrence of blisters and cracks during soldering is prevented in the thin resin-encapsulated semiconductor devices encapsulated by such resin encapsulating materials, which however are poor in releasability and storage stability, so that they are difficult to mold continuously and are unreliable in moisture resistance due to voids occurring on their surfaces.